Open heart surgery survival odds better in the afternoon than morning

A recent study published in The Lancet medical journal indicates that open heart surgery appears to be safer in the afternoon than in the morning, because of the body’s internal clock.

Circadian rhythm

A circadian rhythm is any biological process that displays an endogenous, entrainable oscillation of about 24 hours. In other words, a circadian rhythm is the body’s internal clock, which makes us want to sleep at night, and also drives huge changes in the way our bodies work.

Although circadian rhythms are endogenous (“built-in”, self-sustained), they are adjusted (entrained) to the local environment by external cues called zeitgebers (from German, “time giver”), which include light, temperature and redox cycles.

Open heart surgery

In open heart surgery the patient’s heart is opened and surgery is performed on its internal structures.

The most common types of open heart surgery include:

heart bypass surgery (coronary artery bypass graft — CABG);

Heart valve surgery; and

surgery to correct a heart defect present at birth.

During open heart surgery, doctors must usually stop the patient’s heart (connecting the patient to a heart-lung bypass machine), thereby putting the heart under a great deal of stress as the flow of oxygen to the heart tissue is reduced. Complications from this process include: heart attacks, heart failure or death after surgery.

Afternoon surgery

According to the research just published in The Lancet, such complications arose nearly twice as often in patients having morning open heart surgeries than in patients having afternoon open heart surgeries. The researchers attributed this phenomenon to circadian rhythms, which make the heart stronger and better able to withstand surgery in the afternoon than the morning.

The researches discounted the possibility that the phenomenon could be attributed to surgeons being tired in the morning (e.g., doctors’ own circadian rhythms affecting their surgical skills). Specifically, one team experimented on cardiac tissue samples from patients and showed that the tissue beat more readily in the afternoon. Moreover, an analysis of the DNA in the samples found 287 genes whose activity showed circadian rhythms, and preliminary gene-therapy experiments in mice showed that altering the activity of circadian rhythm genes seemed to reduce the risk of death.

In general the risk of a heart attack or stroke is highest first thing in the morning, while the heart and lungs work at their peak in the afternoon.

What this means for you?

Of course it would be impossible for hospitals to conduct all open heart surgery only after lunch, and inability to schedule an afternoon surgery does not justify a patient avoiding (or even unduly delaying) a required, life-saving operation.

That said, high risk patients could definitely benefit from scheduling their heart surgeries in the afternoon. For example, patients with obesity and/or type 2 diabetes are already more prone to developing complications after open heart surgery.

Researchers are also now investigating whether circadian rhythms have an impact on survival rates in other types of surgery.